1. Field of the Invention
The present invention relates to a water-soluble anionic polymer and, more particularly, to a water-soluble anionic graft copolymer of xanthan gum and polyacrylamide wherein at least part of the amide function of the acrylamide portion of the copolymer is sulfomethylated and wherein the xanthan gum portion of the copolymer is substantially unreacted with formaldehyde.
2. Description of the Prior Art
Sulfomethylation of the amide function of polyacrylamide by means of formaldehyde and sodium bisulfite has been described by Schiller et al., Industrial and Engineering Chemistry, Vol. 48, 1956, pp. 2132-2137.
The preparation of a graft copolymer of xanthan gum and an acrylic monomer which may be acrylamide is described in U.S. Pat. No. 3,708,446 to Pettitt.
The use of formaldehyde to modify hydrophilic colloids such as xanthan gum, starch and guar gum is known. Formaldehyde-modified starch is described in an article by Hullinger in "Starch: Chemistry and Technology", Vol. II, Academic Press, 1967, pp. 445-449, while the use of formaldehyde to increase the viscosity of guar gum (increase in viscosity is due to cross-linking) is described in U.S. Pat. No. 2,730,505. Formaldehyde-modified xanthan gum is described in U.S. Pat. No. 3,020,207.
3. Objects of the Invention
It is an object of the present invention to provide a water-soluble anionic graft copolymer of xanthan gum and polyacrylamide. A further object is to provide a sulfomethylated graft copolymer of xanthan gum and polyacrylamide. Another object is to provide a method for preparing these graft copolymers. These and other objects of the present invention will be apparent from the following description.